1. Field of the Invention
The invention relates to a collapsible, sectioned, articulated ladder with supporting wheels; a radome ladder for external work on convex buildings, such as radomes and other domes.
2. Description of the Prior Art
A number of ladder designs are described in the literature.
U.S. Pat. No. 1,160,721 describes a ladder for use on a flat roof, with particular reference to agricultural outhouses. This ladder can be moved sideways, and is articulated to enable it to be guided past ventilator shafts and the like, but it is only suitable for flat roofs.
U.S. Pat. No. 3,042,143 discloses a portable, articulated collapsible fire-escape ladder. This ladder is so designed that it can be carried to a window or other opening in the wall of a building to furnish an escape route. This ladder is not suitable for being moved sideways by a person on the ladder, nor for use on a convex surface.
U.S. Pat. No. 3,286,789 refers to a collapsible, articulated ladder, the main purpose of this being that the ladder can be folded together for storage in a cupboard or in the boot of an ordinary private car, and be rapidly folded out to its working position. This ladder can only be used as a conventional straight ladder.
U.S. Pat. No. 3,340,960 describes a portable ladder which can be put together from a number of elements, and it is fitted with wheels which roll on tracks parallel to the wall and along the roof or sidewall of a building. This ladder can be moved by motor power along the track, controlled by an operator working on the ladder. This ladder is placed against the wall in an inclined position, and is, in addition fitted with a straight ladder which has wheels at its upper end, which lie on the roof and can thus roll sideways over the roof when the inclined ladder is moved. The inclined ladder is fitted on a motor-driven wheel unit, a "truck," which runs on the tracks along the building. Several ladders can be fitted and connected together along a wall. As illustrated by FIG. 7 of that patent, the weight of the ladder on the roof will be carried by a wheel and also the inclined ladder. This arrangement does not seem very suitable for a spherical roof. This ladder is asserted to be portable, but in its entirety it must comprise a large and complex system, which cannot be used in the same way as the present invention.
U.S. Pat. No. 3,633,708 describes a rope ladder for use when painting the outside of a spherical structure. This ladder is made of two wire ropes which carry the rungs. Spaced along the ropes there are fitted shafts for a wheel to enable the ladder to be moved sideways. The ladder's two wire ropes are joined together at the top to form a point of fixture. This fixture lies in the top point of the dome. A pre-condition for using this ladder is that it can be laid out from the top of the dome, to which there must be access through the dome, which, according to that patent, is a normal feature of water towers. That patent cannot be used to provide the facilities offered by the present invention.
U.S. Pat. No. 3,837,429 describes motor-driven scaffolding for use around buildings with rounded roofs, for example oil tanks. This scaffolding is held in position by wire ropes around air vents in the middle of the top of the tank. On the section between the roof and wall of the tank there is disposed a tubular element with built-in motor. THe wire rope to the tank's central vent is fixed to the one end of this element, while from the other end, which lies outside the tank, is suspended the scaffolding which is to be used, for example, for painting the tank. That patent differs on several counts from the present invention which will now be described.